Scottish Power Renewables had bid for seven more turbines at the site in Ae Forest.
But Ministers have refused on the recommendations of the Reporter following a public local inquiry held last summer.
After hearing from the applicant, as well as Dumfries and Galloway Council and considering objections from planners, Scottish Natural Heritage and SEPA and six members of the public, the Reporter concluded the extension would have a detrimental impact on the local landscape.
In the formal letter of determination sent to Scottish Power Renewables earlier this month, and now available online, Ministers backed the Reporter’s decision.
The letter said: “With reference to Schedule 9 of the Electricity Act, there would be significant adverse effects on natural beauty.”
It went on: “The Reporter acknowledges the benefits of the development, but identifies the main concerns with regard to the application as the landscape and visual effects. These are a consequence of the prominent nature of the site, its contribution to the setting of mid Annandale, and the contrast in the landscape character of the development site with that of the site of the existing windfarm.
“These impacts mean that the proposal is contrary to the development plan and to the Dumfries and Galloway Wind Farm Landscape Capacity Study.”
The existing Harestanes windfarm comprises 68 turbines and opened in July 2014.